This invention relates to suspension type heat exchangers for effecting drying, preheating, heating and cooling of particulate material, such as cement, alumina, fly ash, etc., incorporated in a gas stream of high temperature, and more particularly it is concerned with an improvement in or relating to the separating chamber of a heat exchanger of the suspension type for separating the particulate material from its carrier gas flow.
One kind of suspension type heat exchanger of the prior art includes a separating chamber of a cylindrical form having a substantially horizontal center axis for separating particulate material from a gas stream, a collecting chamber of a funnel shape located beneath the separating chamber, an inlet duct connected to the separating chamber along the entire length thereof in such a manner that a gas stream is introduced into the separating chamber tangentially of the circumferential surface of the separating chamber, and an outlet duct connected to one end of the separating chamber or two outlet ducts each connected to one of opposite ends of the separating chamber to extend along the center axis of the separating chamber. In the suspension type heat exchanger of the prior art described hereinabove, gas is drawn or induced to flow into the separating chamber along the entire length of the separating chamber, and a spiral stream of gas and particulate material is generated in the whole of the separating chamber. This type of separating chamber has the disadvantage that it is low in the efficiency of collecting particulate material because a portion of the particulate material to be separated from the gas is discharged together with the gas from the separating chamber through the outlet duct or ducts before reaching the inner wall surface of the separating chamber.
Another type of separating chamber of a suspension type heat exchanger of the prior art is in the form of a cyclone. Still another type of separating chamber relies on inertia, collision or gravity for operation. In the separating chamber of the cyclone type, two types of swirling streams, one type being a stream of forced vortex motion and the other type being a stream of semi-free vortex motion, are generated and the two streams interfere with each other, causing a high pressure loss to occur. The discharged gas is formed into a spiral stream in the outlet duct connected to the upper end of the cyclone and flows upwardly in a spiral stream, so that the particulate material in the outlet duct is displaced radially outwardly by centrifugal forces and does not permit heat exchange to take place satisfactorily. The cyclone has a high angle of inclination in its lower portion and consequently the collecting chamber has a large height. Thus, when a suspension type heat exchanger consists of a plurality of stages of heat exchangers or cyclones, the overall height of the heat exchanger assembly becomes very great. In the separating chamber relying on inertia, collision or gravity, particulate material that has been separated from the gas stream is caused to scatter again in the separating chamber as the gas stream changes its direction of movement, causing a reduction in the efficiency of collecting the particulate material separated from its carrier gas.